Gated Thallium Imaging With Multiheaded SPECT Differentiates Attenuation Artifact From Myocardial Injury in Routine Clinical Studies ECG gated myocardial perfusion studies with Tc-99m labelled tracers allow evaluation of regional systolic wall thickening (SWT) in areas of hypoperfusion. However, gated thallium (Tl) images have not gained widespread acceptance, due to its low counts. The advent of multiheaded gamma cameras increases Tl counts, improving image quality, increasing signal to noise ratio and the potential for gated Tl (G-Tl) studies. To determine the utility of G-Tl imaging, we studied 36 consecutive patients (29 men and 7 women) who were referred for Tl stress- redistribution-reinjection imaging using a 3-headed SPECT camera. Thirty pts had CAD and 6 pts had no known CAD. For each pt, the LV was divided into 4 long-axis tomograms encompassing the entire LV and the myocardial Tl activity of 12 comparable regions with systolic wall thickening (SWT) was assessed. In 269 of 284 (95%) mild-moderate (MM, 50-84% of peak normal activity) and 39 of 59 (65%) severely reduced Tl regions (<50% of peak) could be assessed for SWT. Because distinction between attenuation artifact and prior myocardial infarction (MI) is of clinical concern, we directed our attention to the 159 regions with MM fixed Tl defects. SWT was normal in 23 of 27 (85%) regions in pts without CAD compared to only 64 of 132 (48%) regions in pts with known CAD (p<0.01). Abnormal SWT was present in 37 of 68 regions (54%) in pts with ECG Q-waves or MI. These data suggest that routine ECG gating of Tl studies is feasible. Among regions with anomalous reduced mild-moderate fixed Tl defects, SWT in G-Tl may be helpful in distinguishing artifactual Tl defect from true prior injury.